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under the conditions of the experiment: if, by the presentation of molecules of a third chemical substance, there is rendered possible the adoption by the various atoms of another configuration, more stable than that just supposed to be assumed, this, the most stable configuration, will be adopted. But if the earlier stable configuration has been assumed by the atoms, it does not follow that the introduction of the third class of molecules will now cause this configuration to become unstable

41. Following out this line of argument, it would appear probable that compounds should present phenomena somewhat analogous to those exhibited by elements when in the nascent, i.e. on the hypothesis now adopted, atomic state. Let it be supposed that no chemical change occurred when the compound molecules a and 6 were brought into contact, nevertheless if the atoms constituting these molecules were allowed to react a chemical change might occur. In a reaction wherein the given compound is produced there must be a moment of time when this compound can only be said to exist potentially, when the atoms which constitute its molecules have not settled down into stable configurations; at this moment the compound may be said to exist in the nascent state. If the atomic vibrations and interactions are allowed to run what may be called their normal course, the compound molecules are certainly produced, but if these interactions are interfered with, a new set of molecules may be

1 It may be urged that the energy (or part of the energy) which is used in decomposing the molecules of the reacting substances is gained by the atoms thence produced, and that the only difference between e.g. ordinary and nascent' hydrogen, is to be found in the greater chemical energy of the latter. The importance of this point of view is of course admitted by the upholders of the atomic explanation of nascent actions, but they would supplement this by the statement that the configuration with which the greater quantity of energy is associated is atomic, and they contrast this with a molecular and comparatively inactive configuration.

The experiments of Victor Meyer on iodine give direct evidence of the separation of elementary molecules into atoms by the addition of energy in the form of heat. (See ante, p. 31 par. 15.)

In book 11. chapter 11. will be found some facts regarding dissociation which bear on the subject of nascent actions.

formed, which molecules bear a more or less simple genetic relation to those produced in the normal process of chemical change?

The following among other cases of chemical change find a partial explanation in terms of this hypothesis. Nitrous acid has no action on the primary mononitroparaffins (CH2n+2. NO,), but these compounds are converted into nitrolic acids (C,H,n. 1,02) by the action of potassium nitrite and sulphuric acid, i.e. by the action of potentially formed nitrous acid. Nitric acid does not act on napthol to produce dinitronapthol, but if napthol be produced in contact with nitric acid-e.g. by boiling diazonapthalene hydrochloride in presence of nitric acid-dinitronapthol is formed. Carbon monoxide and ethylene do not react to form acrolein even under the influence of electric sparks, but if ethylene is exploded with a quantity of oxygen less than sufficient for complete oxidation, carbon monoxide is produced and simultaneously acrolein is formed, i.e. the chemical change proceeds partly in its normal way and at the same time the atoms of the 'nascent' carbon oxide react on the ethylene molecules with production of acrolein. When pariodophenol is fused with potash at 163o hydroquinone is produced, but at higher temperatures only resorcin is formed: now as fusing potash does not act on hydroquinone it seems necessary to conclude, that in the fusion of pariodophenol at high temperatures hydroquinone is produced, but is immediately changed into resorcin. Many olefines (e.g. amylene) are polymerised by the action of sulphuric acid : the most probable explanation of this action assumes that an unstable compound of olefine and sulphuric acid is produced and again decomposed, and that the molecules

1 In all such considerations we can deal with molecular phenomena only by a statistical method, we can reason only as to the average condition of the mass of molecules constituting a substance at any moment of time.

It seems not improbable that there may sometimes be as great differences between the properties of a number of elementary atoms all of one kind and the elementary molecules which are produced by the union of these atoms, as between the properties of a number of atoms of different kinds and the compound molecules produced by the union of these atoms.

of olefine as they are set free from this compound coalesce to form polymeric molecules. By carrying the explanation a little further, and supposing that this coalescence of molecules is due to the interaction of the atoms, or possibly of groups of atoms, which under ordinary conditions would produce molecules of olefine, the phenomenon in question is brought under the general hypothesis of nascent state. I have myself shewn that bismuthic oxide (Bi,O,) is reduced to bismuthous oxide (Bi,O,) by heating in hydrogen at a temperature lower than that at which hypobismuthic oxide (Bi,O.) is reduced to the same final state, and that hypobismuthic oxide is reduced to hypobismuthous oxide (Bi,O,) at a temperature lower than that at which bismuthous oxide undergoes a similar change. I have also shewn that bismuthic oxide is more easily and completely deoxidised when heated in chlorine than bismuthous oxide. When the atoms composing bismuthic oxide molecules are shaken asunder, the action between these and hydrogen, or chlorine, proceeds until a stable configuration is reached; those points in the molecular series known as hypobismuthic and bismuthous oxide respectively, are passed through during the change, but the molecules of these compounds are only potentially, not actually formed: when however these molecules have been formed before chemical action begins, a higher temperature must be reached before the action actually occurs.

42. Whether or not a given phenomenon is to be explained by the particular application of the molecular theory now under consideration, must be decided by the nature of that phenomenon. Among phenomena which are usually but not invariably explained thus, those which occur in the decomposition of acids by metals are of great importance.

The products of the action of metals on sulphuric and nitric acid, respectively, have been already broadly stated. That no hydrogen is evolved in the case of nitric acid is generally sought to be explained by assuming that the hydrogen atoms are seized by the nitric acid and oxidised to water, with a corresponding reduction of the acid to oxides of nitrogen, nitrogen, and sometimes ammonia.

Direct proof in favour of this hypothesis has been given by Gladstone and Tribe', who have shewn that when a small piece of magnesium is placed in a large excess of nitric acid (strengths 1:1 and 1:2-acid to water-were employed) the gas at first evolved consists of nearly pure hydrogen, but that oxides of nitrogen are very quickly produced. The same chemists have established a close relation between the action on sulphuric and nitric acids of the hydrogen produced by electrolysis of these acids, and hydrogen occluded by platinum or palladium; they have also shewn that hydrogen evolved by the action of the copper zinc couple is very analogous in general reducing actions to hydrogen occluded by platinum or palladium.

When concentrated nitric acid is subjected to electrolysis no hydrogen is evolved, but the acid is reduced; when more dilute acid is used hydrogen is evolved, reduction of the acid also occurs, and the more rapid the electrolysis the greater the quantity of hydrogen evolved. Concentrated nitric acid rapidly acts on hydrogen occluded by platinum or palladium, with oxidation of the hydrogen and reduction of the acid. In the electrolysis of concentrated sulphuric acid sulphur is produced, a portion of the hydrogen formed is oxidised and a portion escapes, and the stronger the battery power the greater is the quantity of hydrogen evolved. When the electrolysis is extremely slow, no hydrogen is evolved, and sulphur dioxide is produced in small quantity unmixed with free sulphur. Hydrogen occluded by palladium or platinum also reduces sulphuric acid, with production of sulphur dioxide and escape of a portion of the hydrogen.

Gladstone and Tribe regard the metal (platinum or palladium) present in their experiments as instrumental in the chemical change. They think that the hydrogen produced is occluded by the metal and again given off to the acid, and that if the gas is produced more quickly than it can be occluded the excess escapes oxidation by the acid: it is probable that occluded hydrogen forms a compound with the occluding metal, and that therefore hydrogen coming from this source is for the most part in the nascent, i.e. atomic state. Their experiments certainly establish the fact that maximum reduction of either acid is obtained when hydrogen is evolved therein near an electro-negative metal; but a comparison of the results with occluded and electrolytically evolved hydrogen shews that the reducing action of the latter on sulphuric acid is more complete than that of the former.

1 C. S. Journal Trans. for 1879. 178. ? C. S. Journal Trans. for 1878. 139 and 306.

The facts, taken as a whole, concerning the action of metals on nitric acid are more in keeping with the hypothesis of the intervention of nascent hydrogen than with the older view, which regarded the various gaseous products as direct results of the deoxidising action of the metal. Indeed to formulate the reaction of zinc on nitric acid on the latter hypothesis, requires that nitric acid should be regarded as a variable compound of nitrogen pentoxide and water, and necessitates considerable skill in the manipulation of formulæ'. The action of copper on concentrated sulphuric acid has been studied by Pickering? The ease with which this acid undergoes deoxidation is shewn by the slow production of cuprous sulphide even at 20°; the equation

5Cu+41,50=Cu.S+ 3CuSO, +4H,0, which represents the change as consisting in deoxidation of part of the acid, and does not involve, nor, according to Pickering's experiments allow, an intermediate stage wherein hydrogen reacts on the acid, being nearly realized. At higher temperatures sulphur dioxide is evolved, until at about 270° the action consists entirely of a change which may be formulated as

Cu+2H, SO,=CuSO,+SO, +2H,0,

4

1 Deville, Compt. rend. 70, 20 & 550; or in abstract, Watts's Dict. Suppl. 2, 304. See also Acworth and Armstrong, C. S. Journal, vol. 2. sor 1877, 54,

et seq.

2 C. S. Journal Trans. for 1878. 112.

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